1. Field of the Invention
The present invention relates to novel chiral ligands derived from ferrocenes and catalysts prepared therefrom for applications in asymmetric catalysis. More particularly, the present invention relates to transition metal complexes of these chiral phosphine ligands. The transition metal complexes according to the present invention are useful as catalysts in asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition; epoxidation, kinetic resolution and [m+n] cycloaddition.
2. Description of the Prior Art
Molecular chirality plays an important role in science and technology. The biological activities of many pharmaceuticals, fragrances, food additives and agrochemicals are often associated with their absolute molecular configuration. A growing demand in pharmaceutical and fine chemical industries is to develop cost-effective processes for the manufacture of single-enantiomeric products. To meet this challenge, chemists have explored many approaches for acquiring enantiomerically pure compounds ranging from optical resolution and structural modification of naturally occurring chiral substances to asymmetric catalysis using synthetic chiral catalysts and enzymes. Among these methods, asymmetric catalysis is perhaps the most efficient because a small amount of a chiral catalyst can be used to produce a large quantity of a chiral target molecule [Book, Ojima, I., Ed. Catalytic Asymmetric Synthesis, VCH, New York, 1993 and Noyori, R. Asymmetric Catalysis In Organic Synthesis, John Wiley and Sons, Inc., New York, 1994].
Asymmetric hydrogenation accounts for major part of all asymmetric synthesis on a commercial scale. Some dramatic examples of industrial applications of asymmetric synthesis include Monsanto""s L-DOPA synthesis (asymmetric hydrogenation of a dehydroamino acid, 94% ee, 20,000 turnovers with a Rh-DIPAMP complex) [Knowles, W. S. Acc. Chem. Res. 1983, 16, 106], Takasago""s L-menthol synthesis (asymmetric isomerization, 98% ee, 300,000 turnovers with a Rh-BINAP complex) [Noyori, R.; Takaya, H. Acc. Chem. Res. 1990, 23, 345] and Norvatis"" (S)-Metolachlor synthesis (asymmetric hydrogenation of an imine, 80% ee, 1,000,000 turnovers with an Ir-ferrocenyl phosphine complex) [Spindler, F.; Pugin, B.; Jalett, H.-P., Buser, H.-P.; Pittelkow, U.; Blaser, H,-U., Altanta, 1996; Chem. Ind. (Dekker), 1996, 63 and Tongni, A. Angew. Chem.. Int. Ed Engl. 1996, 356, 14575].
Invention of chiral ligands for transition metal-catalyzed reactions plays a critical role in asymmetric catalysis. Not only the enantioselectivity depends on the framework of chiral ligands, reactivities can often be altered by changing the steric and electronic structure of the ligands. Since small changes in the ligand can influence the (delta)(delta)G of the rate-determining step, it is very hard to predict which ligand can be effective for any particular reaction or substrate. Development of new structural motifs is important in the process of ligand development. 
Several important chiral phosphines have been studied during 30 years. Knowles"" DIPAMP [Knowles, W. S.; Sabacky, M. J.; Vineyard, B. D. J. Chem. Soc., Chem. Commun. 1972, 10] and Kagan""s DIOP [Kagan, H. B.; Dang, T.-P. J. Am. Chem. Soc. 1972, 94, 6429] ligands were reported for Rh (I)-catalyzed asymmetric hydrogenation at about the same time. The great success in asymmetric hydrogenation of dehydroamino acids has stimulated continuing research on new chiral phosphine ligands. Various bidentate chiral diphosphines such as Chiraphos (Bosnich)[Fryzuk, M. D.; Bosnich, B. J. Am. Chem. Soc. 1977, 99, 6262], BPPM (Achiwa, Ojima) [(a) Achiwa, K. J. Am. Chem. Soc. 1976, 98, 8265. (b) Ojima, I.; Yoda, N. Tetrahedron Lett. 1980, 21, 1051], DegPhos (Nagel)[Nagel, U.; Kinzel, E.; Andrade, J.; Prescher, G. Chem. Ber. 1986, 119, 3326] and ferrocenyl chiral phosphines (Hayashi, Kumada, Ito)[Hayashi, T.; Kumada, M. Acc. Chem. Res., 1982, 15, 395] were discovered. Two excellent ligands come out of extensive ligand studies; BINAP (Otsuka, Nayori and Takayi)[Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.; Souchi, T.; Noyori, R. J. Am. Chem. Soc. 1980,102,7932. Miyashita, A.; Takaya, H.; Souchi, T.; Noyori, R. Tetrahedron 1984, 40, 1245.] in the early 80""s is one of the most frequently used bidentate chiral phosphines, and DuPhos (Burk)[Burk, M. J.; Feaster, J. E.; Nugent, W. A.; Harlow, R. L. J. Am. Chem. Soc. 1993, 115, 10125] in the early 90""s has also shown impressive enantioselectivities. The Rh, Ru and Ir complexes of these ligands have been used as catalysts for asymmetric hydrogenations of olefins, ketones and imines. These ligands are also useful for other asymmetric reactions such as isomerization, hydroacylation, the Heck reaction, and the Grignard coupling reaction. However, there are still a variety of reactions in which only modest enantioselectivity has been achieved with these ligands, and substrate scope is limited both for hydrogenation and for other reactions. Complementary classes of chiral ligands are needed. Due to the critical role of chiral ligands in reaction activity and selectivity, many new phosphine ligands were invented. The major feature of the new chiral phosphine ligands is their structural diversity where different structural motif is created, ligand complexity increases, and the steric and electronic properties of ligands are more tunable. Some of these ligands include monodentate chiral phosphines (MOP, Hayashi) [Uozumi, Y.; Hayashi, T. J. Am. Chem. Soc. 1991, 113, 9887], ferrocenyl phosphine bearing two different phosphine groups (Togni)[Togni, A. Angew. Chem. Int. Ed. Engl. 1996, 356, 14575], Trost""s chiral bisphosphines [Trost, B. M.; Van Vranken, D. L. Chem. Rev. 1996, 96, 395], mixed N-P ligands [Pfaltz, A. Acc. Chem. Res. 1993, 26, 339], Trans diphosphines (TRAP, Ito) [Sawamura, M.; Kuwano, R.; Ito, Y. Angew. Chem. Int. Ed.Engl. 1994, 33, 111] and phosphinite ligand (BINAPHOS, Takaya) [Sakai, N.; Mano, S.; Nozaki, K.; Takaya, H. J. Am. Chem. Soc. 1993, 115,7033]. These new ligands are effective for several asymmetric reactions: hydrosilylation, hydrogenation of imines, allylic alkylation, Michael addition and hydroformylation.
Although there are few chiral ferrocene phosphines reported in the literature (TRAP, Togni""s ligands and Hayashi""s ligands), lack of systematic studies hinders the broad utilities of chiral ferrocene phosphines for asymmetric catalytic reactions. Some of the advantages of chiral phosphines containing ferrocene backbone include the following:
1) ferrocene phosphines are generally quite stable in air and are in a solid form;
2) phosphines adjacent to a ferrocene group are electron-donating, which can aid certain catalytic reactions; and
3) chiral ferrocene phosphines can be easily generated through enantioselective deprotonation of a Cxe2x80x94H group in the ferrocene, asymmetric reduction of ferrocene alkyl ketones or resolution methods.
The present invention includes new inventive structures derived from ferrocene s. The new ligands have been demonstrated to be effective for a range of asymmetric catalytic reactions, especially asymmetric Pd-catalyzed allylic alkylation and Ag-catalyzed [3+2] cyclization of azomethine ylides.
In broad concept, the present invention includes ferrocene anchored chiral ligands and metal complexes based on such chiral ligands useful in asymmetric catalysis. Accordingly, the present invention includes a ligand selected from the group consisting of compounds represented by the formulas: 
wherein xe2x80x9cbridge Axe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R* xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94CONHxe2x80x94Rxe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OROxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Rxe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94Rxe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94Rxe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(IR)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, Cxe2x95x90O, Cxe2x95x90S, SO2, xe2x80x94PO(OR1)xe2x80x94, xe2x80x94PO(NHR1)xe2x80x94, xe2x80x94PO(NR12)xe2x80x94, Si(R1)2 xe2x80x94Rxe2x80x94*, and xe2x80x94Rxe2x80x94;
wherein xe2x80x9cbridge Bxe2x80x9d has a stereogenic carbon center, wherein said xe2x80x9cbridge Bxe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, and xe2x80x94Rxe2x80x94*;
wherein xe2x80x9cbridge Cxe2x80x9d is selected from the group consisting of: CO, SO2, CHxe2x95x90CH, xe2x80x94CONHR*NHCOxe2x80x94 and xe2x80x94(CH2)nxe2x80x94 wherein n is 0, 1 or 2; and
wherein R1 is selected from the group consisting of: an alkyl, aryl, aralkyl, alkaryl, and a substituted derivative thereof; xe2x80x94Rxe2x80x94 is selected from the group consisting of: an alkylene, arylene and a substituted derivative thereof; and * indicates the presence of a stereogenic carbon center.
The present invention also includes a ligand selected from the group consisting of compounds represented by the formulas: 
wherein R is an alkyl, aryl, substituted alkyl, substituted aryl; Ar is a susbtituted or unsubstituted aryl group; wherein Ar and Rxe2x80x3 together form an extended arene; wherein each Rxe2x80x2 and Rxe2x80x3 is independently selected from the group consisting of: H, alkyl, aryl substituted alkyl, substituted aryl, ester and alkoxy; and wherein Rxe2x80x2xe2x80x94Rxe2x80x3 together form a cyclic alkyl or a extented arene.
The present invention further includes a ligand represented by the formula: 
wherein X is selected from the group consisting of: CO, SO2, (CH2)n wherein n=0, 1 or 2, and CHxe2x95x90CH;
wherein Y is selected from the group consisting of: an alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein X has the same meaning as above; and
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine.
The present invention still further includes a ligand represented by the formula: 
wherein R is selected from the group consisting of: H, alkyl, aryl, substituted alkyl, substituted aryl, silyl, ester, amide, oxazoline and phosphate, with the proviso that R is H when Rxe2x80x2 is not H; Rxe2x80x2 is selected from the group consisting of: H, alkyl, aryl, substituted alkyl and substituted aryl; n is 0 or 1;
Y is selected from the group consisting of: alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine.
The present invention additionally includes a ligand selected from the group consisting of compounds represented by the formulas: 
wherein R is selected from the group consisting of: alkyl, aryl, substituted is alkyl and substituted aryl; Z is selected from the group consisting of: CO, SO2 and xe2x80x94(CH2)nxe2x80x94 wherein n=0, 1 or 2; each A is independently a group containing an sp2 or sp3 hybridized N, O, C or S atom, wherein two A groups form a cyclic compound via a chiral connecting group selected from the group consisting of: xe2x80x94NHR*NHxe2x80x94, xe2x80x94OR*Oxe2x80x94, xe2x80x94SR*Sxe2x80x94, xe2x80x94Binolxe2x80x94 and xe2x80x94CH2R*CH2xe2x80x94; wherein each R* is a chiral alkyl or aryl group.
The present invention also includes a catalyst prepared by a process comprising: contacting a transition metal salt, or a complex thereof, and a ligand selected from the group consisting of compounds represented by: 
wherein xe2x80x9cbridge Axe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94CONHxe2x80x94Rxe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OROxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Rxe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94Rxe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94Rxe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1), xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, Cxe2x95x90O, Cxe2x95x90S, SO2, xe2x80x94PO(OR1)xe2x80x94, xe2x80x94PO(HR1)xe2x80x94, xe2x80x94PO(NR12)xe2x80x94, Si(R1)2xe2x80x94, xe2x80x94Rxe2x80x94*, and xe2x80x94Rxe2x80x94;
wherein xe2x80x9cbridge Bxe2x80x9d has a stereogenic carbon center, wherein said xe2x80x9cbridge Bxe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, and xe2x80x94Rxe2x80x94*;
wherein xe2x80x9cbridge Cxe2x80x9d is selected from the group consisting of: CO, SO2, CHxe2x95x90CH, xe2x80x94CONHR*NHCOxe2x80x94 and xe2x80x94(CH2)nxe2x80x94 wherein n is 0, 1 or 2; and
wherein R1 is selected from the group consisting of: an alkyl, aryl, aralkyl, alkaryl, and a substituted derivative thereof; xe2x80x94Rxe2x80x94 is selected from the group consisting of: an alkylene, arylene and a substituted derivative thereof; and * indicates the presence of a stereogenic carbon center; 
wherein R is an alkyl, aryl, substituted alkyl, substituted aryl; Ar is a susbtituted or unsubstituted aryl group; wherein Ar and Rxe2x80x3 together form an extended arene; wherein each Rxe2x80x2 and Rxe2x80x3 is independently selected from the group consisting of H, alkyl, aryl substituted alkyl, substituted aryl, ester and alkoxy; and wherein Rxe2x80x2xe2x80x94Rxe2x80x3 together form a cyclic alkyl or a extented arene; 
wherein X is selected from the group consisting of: CO, SO2, (CH2)n wherein n=0, 1 or 2, and CHxe2x95x90CH;
wherein Y is selected from the group consisting of: an alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein X has the same meaning as above; and
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine; 
wherein R is selected from the group consisting of: H, alkyl, aryl, substituted alkyl, substituted aryl, silyl, ester, amide, oxazoline and phosphate, with the proviso that R is H when Rxe2x80x2 is not H; Rxe2x80x2 is selected from the group consisting of: H, alkyl, aryl, substituted alkyl and substituted aryl; n is 0 or 1;
Y is selected from the group consisting of: alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine; or 
wherein R is selected from the group consisting of: alkyl, aryl, substituted alkyl and substituted aryl; Z is selected from the group consisting of: CO, SO2 and xe2x80x94(CH2)nxe2x80x94 wherein n=0, 1 or 2; each A is independently a group containing an sp2or sp3 hybridized N, O, C or S atom, wherein two A groups form a cyclic compound via a chiral connecting group selected from the group consisting of: xe2x80x94NHR*NHxe2x80x94, xe2x80x94OR*Oxe2x80x94, xe2x80x94SR*Sxe2x80x94, xe2x80x94Binolxe2x80x94 and xe2x80x94CH2R*CH2xe2x80x94; wherein each R* is a chiral alkyl or aryl group.
The present invention also includes a process for preparation of an asymmetric compound comprising:
contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst prepared by a process comprising: contacting a transition metal salt, or a complex thereof, and a ligand selected from the group consisting of compounds represented by: 
wherein xe2x80x9cbridge Axe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94CONHxe2x80x94Rxe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OROxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Rxe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94Rxe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94Rxe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, Cxe2x95x90O, Cxe2x95x90S, SO2, xe2x80x94PO(OR1)xe2x80x94, xe2x80x94PO(NHR1)xe2x80x94, xe2x80x94PO(NR12)xe2x80x94, Si(R1)2xe2x80x94, xe2x80x94Rxe2x80x94*, and xe2x80x94Rxe2x80x94;
wherein xe2x80x9cbridge Bxe2x80x9d has a stereogenic carbon center, wherein said xe2x80x9cbridge Bxe2x80x9d is selected from the group consisting of: xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR* Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, and xe2x80x94Rxe2x80x94*;
wherein xe2x80x9cbridge Cxe2x80x9d is selected from the group consisting of: CO, SO2, CHxe2x95x90CH, xe2x80x94CONHR*NHCOxe2x80x94 and xe2x80x94(CH2)nxe2x80x94 wherein n is 0, 1 or 2; and
wherein R1 is selected from the group consisting of: an alkyl, aryl, aralkyl, alkaryl, and a substituted derivative thereof; xe2x80x94Rxe2x80x94 is selected from the group consisting of: an alkylene, arylene and a substituted derivative thereof; and * indicates the presence of a stereogenic carbon center; 
wherein R is an alkyl, aryl, substituted alkyl, substituted aryl; Ar is a susbtituted or unsubstituted aryl group; wherein Ar and Rxe2x80x3 together form an extended arene; wherein each Rxe2x80x2 and Rxe2x80x3 is independently selected from the group consisting of: H, alkyl, aryl substituted alkyl, substituted aryl, ester and alkoxy; and wherein Rxe2x80x2xe2x80x94Rxe2x80x3 together form a cyclic alkyl or a extented arene; 
wherein X is selected from the group consisting of: CO, SO2, (CH2)n wherein n=0, 1 or 2, and CHxe2x95x90CH;
wherein Y is selected from the group consisting of: an alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W xe2x80x94
wherein W is represented by the formula: 
wherein X has the same meaning as above; and
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine; 
wherein R is selected from the group consisting of: H, alkyl, aryl, substituted alkyl, substituted aryl, silyl, ester, amide, oxazoline and phosphate, with the proviso that R is H when Rxe2x80x2 is not H; Rxe2x80x2 is selected from the group consisting of: H, alkyl, aryl, substituted alkyl and substituted aryl; n is 0 or 1;
Y is selected from the group consisting of: alkyl, aryl, substituted alkyl, substituted aryl and a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein said xe2x80x9clinkerxe2x80x9d is selected from the group consisting of: xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl and ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from the group consisting of: aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine; or 
wherein R is selected from the group consisting of: alkyl, aryl, substituted alkyl and substituted aryl; Z is selected from the group consisting of: CO, SO2 and xe2x80x94(CH2)nxe2x80x94 wherein n=0, 1 or 2; each A is independently a group containing an sp2 or sp3 hybridized N, O, C or S atom, wherein two A groups form a cyclic compound via a chiral connecting group selected from the group consisting of: xe2x80x94NHR*NHxe2x80x94, xe2x80x94OR*Oxe2x80x94, xe2x80x94SR*Sxe2x80x94, xe2x80x94Binolxe2x80x94 and xe2x80x94CH2R*CH2xe2x80x94; wherein each R* is a chiral alkyl or aryl group.
The present invention also includes a chiral ferrocene derivative, chiral carboxyferrocenyl diaryl phosphine, which is useful as an intermediate in the preparation of the ligands of the present invention. The chiral carboxyferrocenyl diaryl phosphine represented by the formula: 
wherein each Ar is independently selected from the group consisting of phenyl and an aryl of 6 to 22 carbon atoms.
The present invention further includes a process for preparing the above chiral carboxyferrocenyl diaryl phosphine as well as processes for:
(1) preparing (S, S, S, S)-FAP 6 ligand, which comprises the step of contacting a carboxyferrocenyl diaryl phosphine and (1S, 2S)-diaminocyclohexane under reaction conditions sufficient to produce said (S, S, S, S)-FAP 6 ligand; and
(2) preparing (S, R, R, S)-FAP 7 ligand comprising the step of contacting a carboxyferrocenyl diaryl phosphine and (1R, 2R)-diaminocyclohexane under reaction conditions sufficient to produce said (S, R, R, S)-FAP 7 ligand.
Several new classes of chiral phosphines with ferrocene backbones are developed for asymmetric catalytic reactions. A variety of asymmetric reactions, such as, hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition, epoxidation, kinetic resolution and [m+n] cycloaddition were developed with these chiral ligands systems. Ag- and Cu- catalyzed [3+2] cyclization reactions were discovered. It was also discovered that Ag (I) complexes in combination with chiral ferrocene phosphines were efficient asymmetric catalysts for the [3+2] cyclization reaction.
Representative examples of chiral phosphine ligands having a ferrocene anchor are depicted below: 
Ferrocene anchors are useful for constructing chiral phosphine ligands. Some of these chiral phosphines have been used in commercial applications of asymmetric catalysts. Lack of systematic studies of ferrocene phosphine ligands limits the applications of these ligands. Structurally innovative new chiral ferrocene phosphines are disclosed in this invention. Many examples of these ligands are provided to demonstrate the scope of the invention. For example, Pd-catalyzed allylic alkylation and kinetic resolution have been achieved using these ferrocene chiral phosphines. Several of these chiral ferrocene phosphine ligands are used for a variety of asymmetric catalytic reactions, including Cu and Ag-catalyzed [3+2] cyclization of azomethine ylides.
In a preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
wherein xe2x80x9cbridge Axe2x80x9d can be a group, such as, xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94R*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94,xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94CONHxe2x80x94Rxe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OROxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94Rxe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Rxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94Rxe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94Rxe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, Cxe2x95x90O, Cxe2x95x90S, SO2, xe2x80x94PO(OR1)xe2x80x94, xe2x80x94PO(NHR1)xe2x80x94, xe2x80x94PO(NR12)xe2x80x94, Si(R1)2xe2x80x94, xe2x80x94Rxe2x80x94*, or xe2x80x94Rxe2x80x94;
wherein xe2x80x9cbridge Bxe2x80x9d has a stereogenic carbon center; xe2x80x9cbridge Bxe2x80x9d can be a group, such as, xe2x80x94CONHxe2x80x94R*xe2x80x94NHCOxe2x80x94, xe2x80x94COxe2x80x94OR*Oxe2x80x94COxe2x80x94, xe2x80x94COR*xe2x80x94COxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94R*xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CH2NHxe2x80x94R*xe2x80x94NHCH2xe2x80x94, xe2x80x94CH2NHCOxe2x80x94R*xe2x80x94CONHCH2xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94R*xe2x80x94NHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94R*xe2x80x94CONHC*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHxe2x80x94RNHxe2x80x94C*H(R1)xe2x80x94, xe2x80x94C*H(R1)NHCOxe2x80x94Rxe2x80x94CONHC*H(R1)xe2x80x94, or xe2x80x94Rxe2x80x94*;
wherein xe2x80x9cbridge Cxe2x80x9d can be a group, such as, CO, SO2, CHxe2x95x90CH, xe2x80x94CONHR*NHCOxe2x80x94 or xe2x80x94(CH2)nxe2x80x94 wherein n is 0, 1 or 2; and
wherein R1 can be a group, such as, an alkyl, aryl, aralkyl, alkaryl, or a substituted derivative thereof; xe2x80x94Rxe2x80x94 can be an alkylene, arylene or a substituted derivative thereof; and * indicates the presence of a stereogenic carbon center.
Preferably, R1 is an alkyl, aryl, aralkyl or alkaryl of 1 to 22 carbon atoms, and each R1 optionally has one or more substituents, each independently selected from halogen, ester, ketone, carboxylic acid, hydroxy, alkoxy, aryloxy, thiol, alkylthio and dialkylamino.
Preferably, xe2x80x94Rxe2x80x94 can be xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl or ferrocene, and wherein each xe2x80x94Rxe2x80x94 optionally has one or more substituents, each independently selected from aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine.
The ligands of the present invention can be a racemic mixture of enantiomers. Preferably, the ligand is a non-racemic mixture of enantiomers, and more preferably, the ligand is one of the enantiomers. Preferably, the ligand has an optical purity of at least 85% ee, and more preferably, the ligand has an optical purity of at least 95% ee.
Preferably, the ligand is selected from compounds represented by the formulas: 
In another preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
wherein R is an alkyl, aryl, substituted alkyl, substituted aryl; Ar is a susbtituted or unsubstituted aryl group; wherein Ar and Rxe2x80x3 together form an extended arene; wherein each Rxe2x80x2 and Rxe2x80x3 is independently selected from H, alkyl, aryl substituted alkyl, substituted aryl, ester and alkoxy; and wherein Rxe2x80x2xe2x80x94Rxe2x80x3 together form a cyclic alkyl or a extented arene.
In still another preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
In yet another preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
wherein X can be CO, SO2, (CH2)n wherein n=0, 1 or 2, or CHxe2x95x90CH;
wherein Y can be an alkyl, aryl, substituted alkyl, substituted aryl or a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein X has the same meaning as above; and
wherein the xe2x80x9clinkerxe2x80x9d can be xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl or ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid and phosphine.
The preferred ligands of this embodiment include compounds represented by the formulas: 
In another preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
wherein R can be H, alkyl, aryl, substituted alkyl, substituted aryl, silyl, ester, amide, oxazoline or phosphate, with the proviso that R is H when Rxe2x80x2 is not H; Rxe2x80x2 can be H, alkyl, aryl, substituted alkyl or substituted aryl; n is 0 or 1;
Y can be alkyl, aryl, substituted alkyl, substituted aryl or a group represented by the formula:
xe2x80x94(linker)xe2x80x94W 
wherein W is represented by the formula: 
wherein the xe2x80x9clinkerxe2x80x9d can be xe2x80x94(CH2)nxe2x80x94 where n is an integer in the range of from 1 to 8, 1,2-divalent phenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-biphenyl, 2,2xe2x80x2-divalent-1,1xe2x80x2-binaphthyl or ferrocene, and wherein each xe2x80x9clinkerxe2x80x9d optionally has one or more substituents, each independently selected from aryl, alkyl, halogen, ester, ketone, sulfonate, phosphonate, hydroxy, alkoxy, aryloxy, thiol, alkylthiol, nitro, amino, vinyl, substituted vinyl, carboxylic acid, sulfonic acid or phosphine.
The preferred ligands of this embodiment include compounds represented by the formulas: 
In still another preferred embodiment, the ligand of the present invention includes compounds represented by the formulas: 
wherein R can be alkyl, aryl, substituted alkyl or substituted aryl; Z can be CO, SO2 and xe2x80x94(CH2)nxe2x80x94 wherein n=0, 1 or 2; each A is independently a group containing an sp2 or sp3 hybridized N, O, C or S atom, wherein two A groups form a cyclic compound via a chiral connecting group which can be xe2x80x94NHR*NHxe2x80x94, xe2x80x94OR*Oxe2x80x94, xe2x80x94SR*Sxe2x80x94, xe2x80x94Binolxe2x80x94 or xe2x80x94CH2R*CH2xe2x80x94; wherein each R* is a chiral alkyl or aryl group.
Preferably, the R* group is 1,2-divalent phenyl and 2,2xe2x80x2-divalent-1,1xe2x80x2binaphthyl.
The preferred ligands of this embodiment include compounds represented by the formulas: 
The design and synthesis of new chiral ligands remains an important area of research with respect to developing highly enantioselective transition metal catalyzed reactions. A successful ligand should therefore be readily accessible, stable, and highly tunable since modification of the ligands steric and electronic properties are often necessary for achieving high asymmetric induction Ligand families derived from effective chiral synthons with the aim of meeting the above-mentioned requirements.
One synthon of chiral ferrocene phosphines is made in this invention and it is derived from the well-known chiral phosphinoferrocenyloxazoline [Richards, C. J.; Damalidis, T.; Hibbs, D. E.; Hursthouse, M. B. Synlett 1995, 74, Nishibayashi, Y.; Uemara, S. Synlett 1995, 79]. The phosphine acid with a chiral ferrocene backbone, i.e., chiral carboxyferrocenyl diaryl phosphine, can be prepared in large quantities and it is an air-stable solid. 
Ligand modifications can then be easily realized by appending various units to the carboxylate functionality. This can be achieved most directly by coupling the ferrocene acid with a variety of amines (chiral or achiral), alcohols (chiral or achiral) using reliable straightforward chemistry. Furthermore, the planar chirality of ferrocene, usually in conjunction with additional sources of chirality, has proven to be quite an effective framework for providing high asymmetric induction.
While the (S) carboxylferrocenyl diaryl phosphine shown above can be made from oxazolinoferrocenyl derived from (S)-vanlinol, the corresponding (R) carboxylferrocenyl diaryl phosphine can be prepared from oxazolinoferrocenyl derived from (R)-vanlinol. 
The first ligands discussed are readily obtained by coupling ferrocene phosphine acid with (1S, 2S) and (1R, 2R)-diaminocyclohexane coupling to produce ferrocene amide phosphine (FAP). These ligands are very successful in inducing high asymmetric induction for a variety of substrates in the Pd-catalyzed allylic substitution reaction. The goal for designing these ligands was to discern the effect of planar chirality in conjunction with the chirality of the diaminocyclohexane backbone. More importantly, since the ligand possesses the planar chiral ferrocene unit, achiral backbones can also be used. These ligands are structurally different from Trost ligand (FIG. A) for asymmetric reactions.
Accordingly, the present invention also includes a process for preparing a chiral carboxyferrocenyl diaryl phosphine represented by the formula: 
wherein each Ar is independently selected from phenyl and an aryl of 6 to 22 carbon atoms. The process comprises the steps of:
providing a chiral oxazolinoferrocenyl diaryl phosphine derived from (S)-vanlinol;
sequentially contacting the chiral oxazolinoferrocenyl diaryl phosphine phosphine derived from (S)-vanlinol and:
(1) water and anhydrous sodium sulfate;
(2) trifluoroacetic acid; and
(3) an acylating agent;
to produce an N-acylated (S)-vanlinol ester of carboxyferrocenyl diaryl phosphine; and
contacting the N-acylated (S)-vanlinol ester of carboxyferrocenyl diaryl phosphine, potassium tertiary butoxide and water to produce the chiral carboxyferrocenyl diaryl phosphine.
Preferably, (S)-oxazolinoferrocenyl diaryl phosphine derived from (S)-vanlinol is formed by a process comprising the steps of:
contacting ferrocenyl chloride and (S)-vanlinol in the presence of a base to produce a ferrocene amide;
contacting the ferrocene amide and an alkyl or aryl sulfonyl chloride to produce a ferrocene oxazoline; and
contacting the ferrocene oxazoline with an organolithium reagent and thereafter with a diarylhalophosphine to produce said chiral oxazolinoferrocenyl diaryl phosphine.
Preferably, the diarylhalophosphine is PPh2Cl, P(xylyl)2Cl or P(ph)(xylyl)Cl and the acylating agent is acetic anhydride.
The present invention still further includes a process for:
(1) preparing (S, S, S, S)-FAP 6 ligand, which comprises the step of contacting a carboxyferrocenyl diaryl phosphine and (1S, 2S)-diaminocyclohexane under reaction conditions sufficient to produce said (S, S, S, S)-FAP 6 ligand; and
(2) preparing (S, R, R, S)-FAP 7 ligand comprising the step of contacting a carboxyferrocenyl diaryl phosphine and (1R, 2R)-diaminocyclohexane under reaction conditions sufficient to produce said (S, R, R, S)-FAP 7 ligand.
The FAP 6 or FAP 7 ligands prepared by the above processes have an optical purity of at least 85% ee, preferably at least 95% ee.
The present invention also includes a catalyst prepared by a process comprising contacting a transition metal salt, or a complex thereof, and a ligand according to the present invention. The catalyst may be prepared in situ or as an isolated compound.
The catalyst of the present invention can be a racemic mixture of enantiomers. Preferably, the catalyst is a non-racemic mixture of enantiomers, and more preferably, the catalyst is one of the enantiomers. Preferably, the catalyst has an optical purity of at least 85% ee, and more preferably, the catalyst has an optical purity of at least 95% ee.
Suitable transition metals for the preparation of the catalyst include Ag, Pt, Pd, Rh, Ru, Ir, Cu, Ni, Mo, Ti, V, Re and Mn.
As mentioned above, the catalyst can be prepared by contacting a transition metal salt or its complex and a ligand according to the present invention.
Suitable transition metal salts or complexes include the following:
AgX; Ag(OTf); Ag(OTf)2; AgOAc; PtCl2; H2PtCl4; Pd2(DBA)3; Pd(OAc)2; PdCl2(RCN)2; (Pd(allyl)Cl)2; Pd(PR3)4; (Rh(NBD)2)X; (Rh (NBD)Cl)2; (Rh(COD)Cl)2; (Rh(COD)2)X; Rh(acac)(CO)2; Rh(ethylene)2(acac); (Rh(ethylene)2Cl)2; RhCl(PPh3)3; Rh(CO)2Cl2; RuHX(L)2(diphosphine), RuX2(L)2 (diphosphine), Ru(arene)X2(diphosphine), Ru(aryl group)X2; Ru(RCOO)2(diphosphine); Ru(methallyl)2(diphosphine); Ru(aryl group)X2(PPh3)3; Ru(COD)(COT); Ru(COD)(COT)X; RuX2(cymen); Ru(COD)n; Ru(aryl group)X2(diphosphine); RuCl2(COD); (Ru(COD)2)X; RuX2(diphosphine); RUCl2(xe2x95x90CHR)(PRxe2x80x23)2; Ru(ArH)Cl2; Ru(COD)(methallyl)2; (Ir (NBD)2Cl)2; (Ir(NBD)2)X; (Ir(COD)2Cl)2; (Ir(COD)2)X; CuX (NCCH3)4; Cu(OTf); Cu(OTf)2; Cu(Ar)X; CuX; Ni(acac)2; NiX2; (Ni(allyl)X)2; Ni(COD)2; MoO2(acac)2; Ti(OiPr)4; VO(acac)2; MeReO3; MnX2 and Mn(acac)2; wherein each R and Rxe2x80x2 is independently selected from alkyl or aryl; Ar is an aryl group; and X is a counteranion.
In the above transition metal salts and complexes, L is a solvent and the counteranion X can be halogen, BF4, B(Ar)4 wherein Ar is fluorophenyl or 3,5-di-trifluoromethyl-1-phenyl, ClO4, SbF6, PF6, CF3SO3, RCOO or a mixture thereof.
In another aspect, the present invention includes a process for preparation of an asymmetric compound using the catalysts described above. The process includes the step of contacting a substrate capable of forming an asymmetric product by an asymmetric reaction and a catalyst according to the present invention prepared by contacting a transition metal salt, or a complex thereof, and a ligand according to the present invention.
Suitable asymmetric reactions include asymmetric hydrogenation, hydride transfer, allylic alkylation, hydrosilylation, hydroboration, hydrovinylation, hydroformylation, olefin metathesis, hydrocarboxylation, isomerization, cyclopropanation, Diels-Alder reaction, Heck reaction, isomerization, Aldol reaction, Michael addition; epoxidation, kinetic resolution and [m+n] cycloaddition wherein m=3 to 6 and n=2.
Preferably, the asymmetric reaction is hydrogenation and the substrate to be hydrogenated is an ethylenically unsaturated compound, imine, ketone, enamine, enamide, and vinyl ester. Suitable catalysts for the hydrogenation of ketones to produce a chiral alcohol include chiral ruthenium complex with a PNNP ferrocene ligand according to the present invention. Suitable catalysts for the silver-catalyzed asymmetric [3+2] cycloaddition of, for example, an azomethine ylide with a dipolarophile, is the Ag-Xyl-FAP catalyst, which can be prepared from AgOAc or Xyl-FAP ligand.
Preferably, the asymmetric reaction is allylic alkylation and the substrate is an allylic ester. Also preferably, the asymmetric reaction is a kinetic resolution reaction and the substrate is a racemic allylic ester.
The Pd-catalyzed allylic alkylation reaction has become the standard test reaction for gauging the effectiveness of new ligands [Pfaltz, A.; Lautens, M., in Comprehensive Asymmetric Catalysis; Jacobsen, E. N.; Pfaltz, A.; Yamamoto, H., Eds.; Springer-Verlag: Berlin, 1999, Vol. III, Chapter 24, pp. 833-884].
A preferred catalyst for the asymmetric allylic alkylation of an allylic ester substrate is ferrocene amide phosphine (FAP), which is a palladium catalyst according to the present invention. This ligand has been very successful in inducing high asymmetric induction for a variety of substrates in the Pd-catalyzed allylic substitution reactions.
Allylic alkylation of an allylic ester substrate under kinetic resolution conditions, i.e., allylic alkylation of a racemic mixture of an allylic ester substrate with a non-racemic palladium catalyst according to the present invention, only a single enantiomer is preferentially allylically alkylated. This reaction produces not only an enantiomerically enriched allylically alkylated product, but also an enantiomerically enriched unreacted allylic ester.
Specifically, (E)-1,3-diphenylprop-2-enyl acetate has been the substrate most often used and numerous ligands have been successfully applied to the enantioselective alkylation of this compound. With more challenging cycloalkenyl ester substrates, far fewer successful ligands have been reported. Employing FAP ligands, high enantioselectivities can be achieved for both (E)-1,3-diphenylprop-2-enyl acetate and cycloalkenyl ester.
Using dimethyl malonate as nucleophile and a chiral FAP ligand, the reaction conditions were optimized (see Table 1, below). Several of the commonly used bases for allylic alkylation were investigated with the combination of BSA and KOAc proving most effective. Further improvement of enantioselectivity was achieved when the reaction was carried out in THF. The reaction seemed to proceed quickly to product within the first few hours then slowed significantly or ceased altogether. This observation also coincided with formation of a precipitate from the reaction solution.
A very efficient kinetic resolution of cycloalkenyl ester is occurring with a Pd-FAP catalyst (table 2). For example, after 54% conversion, unreacted allylic acetate has an enantiomeric excess of 99% and the alkylation product has an enantiomeric excess of 92%. Using the reported equation for measuring kinetic resolution efficiency this gives S=61. An additional 20 hours of reaction time results only in a further 20% reaction conversion.
In tables 3-4, the reactivity and enantioselectivity increase as the size of the alkali metal increases, reaching a maximum with Cs+. Alkylation of the xe2x80x9cstandardxe2x80x9d (E)-1,3-diphenylprop-2-enyl ethyl carbonate proceeded with a high enantioselectivity of 93% using one FAP ligand. It is interesting to note that a mismatched FAP gave only a slightly lower enantioselectivity of 87%.
Azomethine ylide 1,3-dipoles react with olefinic dipolarophiles possessing electron withdrawing groups to form highly substituted five-membered ring nitrogen heterocycles [Grigg, R.; Hargreves, S.; Redpath, J.; Turchi, S.; Yogananthan, G. Synthesis 1999, 441]. This extremely versatile and atom economical process has been used towards construction of highly functionalized synthetic intermediates and as a key step in alkaloid natural product syntheses. A practical approach has been formation of N-metallated azomethine ylides [Kanemasa, S.; Tsuge, O. In Advances in Cycloaddition; Curran, D. P., Ed.; Jai Press: Greenwich, 1993; Vol. 3, pp 99-159]. This method allows the cycloaddition to proceed under much milder reaction conditions and in many cases with a high degree of stereocontrol.
In many cases a stoichiometric quantity of Ag(I) salt is employed. Due to the low solubility of most Ag(I) salts, polar coordinating solvents such as CH3CN, DMSO, and DMF are typically used. The reaction is thought to proceed by N, O-coordination of the xcex1-aminoester imine to the transition metal, followed by deprotonation with NEt3 to form the reactive metal-bound azomethine ylide dipole. Coordination of the imine with the metal increases the acidity of the xcex1-hydrogen thus allowing deprotonation by a weak base such as NEt3.
Development of an asymmetric azomethine ylide cycloaddition is important if this methodology is to be truly practical for the synthesis of biologically active compounds. The attractive feature of this process is the simultaneous formation of up to four contiguous chiral centers in one synthetic transformation with a high level of diastereoselectivity.
The present invention includes AgOAc and PPh3 as the catalyst system employed for making the [3+2] products. Prior to the present invention, there had been no reported attempts to study the effect of ligation on the Ag catalyst. Ligation is important because Ag(I) salts have very low solubility in most organic solvents. In order to effectively promote this reaction, Ag(I) salts have been typically used in stoichiometric quantities. However, addition of PPh3 forms a soluble complex with Ag(I) salts in most organic solvents. As a result, the cycloaddition reaction proceeds efficiently with only 1 mol % of catalyst.
All of the racemic pyrrolidine products in the present invention were formed using AgOAc/PPh3 as catalyst. This proved to be a highly reactive and general catalyst system for a variety of azomethine ylide and dipolarophile substrates. In some cases, the products were formed within minutes. This invention disclosed that Cu(I) catalysts, such as CuOAc and Cu(CH3CN)4BF4, complexed with PPh3 were equally as effective. Prior to this study, there were no reports of any catalysts used in such transformation.
In tables 5-9, a number of experiments have been carried out. Some commercially available chiral phosphines were tested. However, the resulting enantioselectivities were very low.
The present invention includes new chiral ferrocene amide phosphines with planar chirality. The Ag complexes with these ligands are effective catalysts for the [3+2] cycloadditions. A variety of dipolarophile substrates and dipole substrates have been tested. The preferred ligand for this reaction is a Xyl-FAP ligand.